In the development of petroleum lubricating oils the trend has been directed to more and more drastic refining methods to reduce the tendency of such oils to form carbon deposits and/or sludge. While such highly refined oils possess many advantages, their resistance to oxidation, particularly under severe operating conditions is generally decreased; they are more prone to form acidic oxidation products which are corrosive, and which cause undesirable increase in the viscosity of the lubricant.
To overcome the tendency of such highly refined oils to form carbon and/or sludge deposits on various operating parts of the engine, such as pistons, piston rings, valves etc., various oil-soluble metal-containing detergent compounds, now well-known in the art, have been incorporated in such lubricating oil compositions. Such metal-containing organic compounds, while effective as detergents for dispersing the precursors of deposits within the oil itself rather than permitting them to form deposits on the engine parts, had the disadvantage of forming ash deposits in the engine. To overcome this disadvantage, so-called ashless detergents were developed, and are now well-known in the art.
The organic compounds, both the metal-containing and the ashless, while imparting detergency properties to the lubricating oils containing the same do not inhibit the oxidation of such lubricating oils at high temperature operating conditions. The compounds of the present invention, hereinafter described, are effective in inhibiting the high temperature oxidation of such lubricating oils.